Elimination or limiting of slack in the tape as it is unwound from the reel in a videocassette has been found to be essential for consistently accurate performance. Slack limiter devices have been devised which exert a mild but adequate restraining or tightening effect on the moving tape at or close to a guide. Looseness and flutter in the tape is thereby controlled in much the same way as a loose drive belt is tightened by a spring-mounted idler pulley.
A typical prior art slack limiter device consists of a section of springy plastic film having a frictionreducing edge covering which is pressed against the tape at an acute angle. The section of film is mounted on the frame of the cassette in such a position that its intermediate portion is slightly bowed, the springiness of the film then urging the covered edge against the tape surface and preventing any momentary loosening.
Mounting of the plastic film on the cassette frame by means of adhesives has not been totally reliable. Accurate placement of the device is uncertain. Under the tension imparted by the springiness of the film, the adhesive bond eventually weakens and either permits the spring tension to decrease or allows the entire device to fall away and into the mechanism.